1. Field of the Invention
The present invention relates to an image and sound reproducing device, and more particularly to an image and sound reproducing device for decoding and reproducing encoded data in which digitally compressed and encoded image data, auxiliary image data such as superimposed characters or the like which is digitally compressed and encoded in the same manner separately from the image data, and sound data which is digitally compressed and encoded in the same manner is multiplexed respectively.
2. Prior Art
Conventionally, there is known an image and sound reproducing device for displaying a main image and an auxiliary image in a superposition manner by subjecting to a decoding processing separately encoded data in which digitally compressed and encoded auxiliary image data such as superimposed characters for films and words for karaoke are multiplexed in addition to normal image data and sound data digitally compressed and encoded (for example, Japanese Patent Application Laid-Open No. 6-314092).
FIG. 1 is a block view showing one example of the conventional image and sound reproducing device which has been described above. This conventional reproducing device reproduces multiplexed encoded data which is recorded on a recording medium 181. On the recording medium 181, auxiliary image data such as character data which is encoded in run-length encoding is multiplexed and recorded in advance in digitally compressed encoded normal image data and sound data.
The reproducing device reproduces encoded data which is recorded and multiplexed in this recording medium 181 and the data separating part 182 separates the data. Then, the auxiliary image data is supplied to an auxiliary image decoding part 183, and the main image data is supplied to a main image decoding part 184 with the result that the main data and the auxiliary data is decoded and processed separately in the auxiliary and main image decoding parts 183 and 184. The decoded auxiliary image data is overlapped with the decoded main image data at the image data superposition part 186 to be output as an image signal. Furthermore, the compressed encoded sound data which is separated at the data separating part 182 is supplied to a sound decoding part 185 and is decoded and processed to be output as a sound signal.
Furthermore, as a synchronization reproduction method of such digital compressed and encoded data, there is the MPEG (Moving Picture Experts Group) method which is an international standard for compressing moving pictures. In the encoded data in the MPEG method, image and sound data, as well as two kinds of time codes which is used for synchronizing and reproducing the sound and image data is multiplexed. One of the time codes is a SCR (System Clock Reference) which is a reference time code for generating a reference clock at the reproducing device while the other time code is s PTS (Presentation Time Stamp) displaying the image data and the sound data and indicating output time.
FIG. 2 is a block view showing one example of the conventional reproducing device on the basis of the MPEG method. The data separating part 192 separates a time code for synchronization control together with the image data and sound data which is reproduced from the recording medium 191. The SCR which is a time code for generating the reference clock is sent to the reference clock generating part 193 and is used for initialization or correction of the reference clock.
Furthermore, the data separating part 192 sends the PTS 1 showing the display time of the auxiliary image to the auxiliary image decoding part 194, and the PTS 2 showing the display time of the main image to the main image processing part 195, and the PTS 3 showing the output time of the sound to the sound decoding part 196 respectively. After the main image decoding part 195 decodes and processes encoded data of the main image which is input through the data separating part 192, the main image decoding part 195 compares the PTS 2 with the reference clock from the reference clock generating part 193 so that the decoded main image data is output to the image data superposition part 197 at the time when the reference clock agrees with the PTS 2.
Furthermore, after the auxiliary image decoding part 194 decodes and processes the encoded data of the auxiliary image which is input through the data separating part 192, the auxiliary image decoding part 194 compares the PTS 1 with the reference clock from the reference clock generating part 193 so that the decoded auxiliary image data is supplied to the image data superposition part 197 at the time when the reference clock agrees with the PTS 1 to be overlapped with the decoded main image data. Furthermore, after the sound decoding part 196 decodes and processes the sound encoded data which is input through the data separating part 192, the sound decoding part 196 compares the PTS 3 with the reference clock from the reference clock generating part 193 to be output at the time when the reference clock agrees with the PTS 3.
However, with the conventional reproducing device, in the case where the reproducing device is realized by means of software, the data processing capability of the reproducing device is lowered with the result that the decoding processing of the auxiliary image data such as superimposed characters and words for karaoke and superposition processing of the auxiliary image data to the main image cannot be carried out in real time in some cases. In such cases, the superposition processing of the auxiliary image is appropriately thinned out (data pieces are thinned out) so that the synchronization correction is required to be carried out.
However, in the conventional reproducing device such as recording and reproducing device for characters and images shown in FIG. 1, the synchronization correction is not carried out in the case where the data processing capability of the reproducing device is lowered and the image cannot be processed in real time.
Furthermore, in the conventional reproducing device shown in FIG. 19 in accordance with the aforementioned MPEG method, the resolution of the SCR which is reference time code for generating the reference clock with the reproducing device is either 90kHz or 27MHz with the result that there is a problem with the precision of the reference clock which is generated in the case where the reproducing device is realized by means of software.